A major manhunt is under way in Helmand province for the rogue Afghan soldier who killed three British soldiers.
The men, serving with 1st Battalion, The Royal Gurkha Rifles, died in Nahr-e Saraj on Tuesday.
Nato said it was using every "asset" within its power to find their killer and those who may be assisting him.
Meanwhile Defence Secretary Liam Fox said the UK was "not desperate" to leave Afghanistan and was there for UK "national security".
Prime Minister David Cameron told the Commons it was an "isolated" case and insisted the UK would continue to train the Afghan army.
One of those killed in the attack has been named locally by MP David Simpson as Neal Turkington from Portadown, County Armagh.
A Royal Marine was also killed on Tuesday when he was shot dead in a separate incident in Helmand province.
The BBC understands one of the three soldiers killed was shot and the other two were killed by a rocket-propelled grenade. The Taliban have claimed the Afghan soldier responsible had joined their insurgency.
On Wednesday, Afghan army spokesman Gen Ghulam Farook Parwani identified the rogue soldier as Talib Hussein, from the minority Hazara community which is usually opposed to the Taliban. He said the man's motive was still unclear.
Brig Gen Josef Blotz, spokesman for the Nato-led International Security Assistance Force (Isaf) in Afghanistan, said the British and Afghan armies trusted each other, and that it was too early to say what changes needed to be made to improve the safety of UK troops.
"Once the result of the investigation is on the table, we need to very diligently screen that, and then come up with recommendations for improvements, perhaps in the area of training, vetting and screening whatsoever," he said.
"But I can't now speculate at this point in time because we have to wait for the report."
A spokesman for the Afghan ministry of defence said local and foreign special forces were being used to hunt the man responsible for shooting the British soldiers.
But Dr Fox dismissed reports the Afghan soldier was a Taliban militant and called for the incident to be kept in proportion.
"We've always recognised the risks that are inherent within partnering and we have worked very hard to reduce these to a minimum," he said.
"But we can never guarantee against the actions of a rogue individual.
"We're also very clear that the benefits outweigh the risks, because it offers the quickest and most effective way of delivering our campaign objectives and, ultimately, having UK forces returning home."
He said the UK was "not desperate to get out, but very keen to hand over to the Afghan authorities their own security".
Speaking during prime minister's question time, David Cameron said: "We need to have an inquiry to get to the bottom of what happened in this tragic, although I believe isolated, case."
About 5,000 British troops were "fully partnered" with Afghan forces, he said.
"When you hear their stories about how well they are working together it really does give you hope that we are building an Afghan army that we will be able to hand over to.
"And we mustn't lose sight of that in spite of all the difficulties."
On Wednesday, four soldiers belonging to Isaf were killed by a bomb in southern Afghanistan. Another US soldier died in a separate insurgent attack elsewhere in the country.
So far in July, 45 international troops have died in Afghanistan, 33 of them from the US.